Dunford’s term doesn’t end until Oct. 1, and Milley’s tenure as Army chief of staff is supposed to run through August 2019.

Trump said the date of transition is “to be determined.”

Trump used an early morning tweet to reveal his choice.

“I am thankful to both of these incredible men for their service to our Country!” he said.

I am pleased to announce my nomination of four-star General Mark Milley, Chief of Staff of the United States Army – as the Chairman of the Joint Chiefs of Staff, replacing General Joe Dunford, who will be retiring....

Fear of missing out?

Fear no longer. Be the first to hear about breaking news, as it happens. You'll get alerts delivered directly to your inbox each time something noteworthy happens in the Military community.

Thanks for signing up.

By giving us your email, you are opting in to our Newsletter: Sign up for the Air Force Times Daily News Roundup

Dunford is a former commandant of the Marine Corps and commander of coalition troops in Afghanistan. Milley commanded troops during several tours in Iraq and Afghanistan.

Dunford’s spokesman, Air Force Col. Patrick Ryder, said all indications are that Dunford will serve his full term. Ryder referred other questions to the White House. He said Dunford congratulated Milley on his nomination.

“He has served with Gen. Milley in peacetime and in combat and has the highest regard for his leadership.”

In a statement, Pentagon spokesman Air Force Lt. Col. Mike Andrews said, "we are aware of the president’s nomination and share his confidence for Gen. Mark Milley, Chief of Staff of the United States Army, to be the Chairman of the Joint Chiefs of Staff. The Department of Defense remains fully focused on defending our nation.”

Sen. Lindsey Graham, R-S.C., a member of the Senate Armed Services Committee, said in a statement that Milley was "a battle-tested commander and Pentagon reformer who will be a worthy successor" to Dunford.

Trump’s decision, announced before leaving Washington for the annual Army-Navy football game in Philadelphia, had caught some in the Pentagon by surprise when unofficial word spread Friday after he said a succession announcement was coming.

Normally an announcement on a new chairman wouldn't be expected until early next year. Officials had said the Air Force chief, Gen. David Goldfein, was also a strong contender for the job.

President Donald Trump, with Secretary of Defense Jim Mattis and Chairman of the Joint Chiefs Gen. Joseph Dunford, stand for the national anthem during a Memorial Day ceremony at Arlington National Cemetery May 28, 2018. Trump on Saturday named Gen. Mark Milley to be Dunford's successor. (Jim Watson/AFP/Getty Images)

Last year he admonished the House Armed Services Committee for its inability to approve a defense budget, slamming it as “professional malpractice.”

In 2016, he told lawmakers, in answer to a direct question, that women should also have to register for the draft now that they are allowed to serve in all combat jobs.

As the Army's top leader, he helped shepherd the groundbreaking move of women into front-line infantry and other combat positions, while warning that it would take time to do it right. More recently, he has worked with his senior officers to reverse a shortfall in Army recruiting when the service fell far short of its annual goal this year.

The Army's chief of staff is proud of the progress the service has made in his tenure, and there are big plans for more.

By: Meghann Myers

He also played a role in one of the Army's more contentious criminal cases. While serving as head of U.S. Army Forces Command at Fort Bragg, North Carolina, Milley was assigned to review the case of former Army Sgt. Bowe Bergdahl, who abandoned his post in Afghanistan and was held captive by the Taliban for five years.

Milley made the early decision to charge Bergdahl with desertion and misbehavior before the enemy. Bergdahl was eventually found guilty, reduced in rank to private, dishonorably discharged and fined $10,000, but was spared any additional prison time.

A native of Winchester, Massachusetts, and a fervent supporter of the Boston Red Sox and other city teams, Milley received his Army commission from Princeton University in 1980. An infantry officer by training, he also commanded Special Forces units in a career that included deployments in the invasion of Panama in 1989, the multinational mission in Bosnia-Herzegovina to implement the Dayton Peace Accords, and the Iraq war.

The Milley move starts a series of military leadership changes in coming months, including successors in 2019 for Adm. John Richardson as the chief of Naval Operations, Gen. Robert Neller as commandant of the Marine Corps, and Air Force Gen. Paul Selva as vice chairman of the Joint Chiefs. Trump also will pick a replacement for Milley as Army chief.

Goldfein began his term as Air Force chief of staff in 2016, so wouldn’t be expected to step down until the summer of 2020.